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KAMPALA (Reuters) - The military chief of the former Congolese M23 rebel group is in Uganda's capital Kampala and his fighters in the western part of the country, Uganda's military said on Sunday, contradicting reports he had gone missing.

Democratic Republic of Congo stepped up army patrols in its volatile east on Saturday after reports from a Congolese governor that Sultani Makenga had vanished from a camp for demobilized fighters in neighboring Uganda. Gunfire erupted outside an important border town.

Another armed uprising in east Congo, which has been plagued by violence for decades, would stir an already unstable cauldron of political tensions facing President Joseph Kabila's government as he reaches the end of his mandate on Dec. 19.

Opposition leaders have called for Kabila to step down, but he had vowed to stay on until elections that keep being delayed and are currently not scheduled to happen until April 2018.

"Makenga is in Kampala and M23 are in Bihanga (military encampment in western Uganda). Let whoever has any information to the contrary prove us wrong," Ugandan military spokesman Paddy Ankunda said by telephone.

He also denied that the Ugandan military had boosted deployments at the border.

Until its defeat in 2013, M23 was the strongest of dozens of armed groups that have continued to control large swaths of mineral-rich eastern Congo despite the end of the 1998-2003 war.

At its peak, it seized North Kivu's capital Goma but following its defeat by U.N. and Congolese troops, many of its fighters fled into Uganda and Rwanda.

They have since lived in military-run camps awaiting amnesties promised under a peace deal.